KR102453415B1 - A method for manufacturing a separator coated with inorganic materials - Google Patents

Abstract

One aspect of the present invention, (a) manufacturing a porous support by processing a composition comprising a first polyolefin and a second polyolefin modified with a crosslinking compound; (b) applying steam to the porous support to crosslink the second polyolefin included in the porous support; (c) preparing a slurry by dissolving the inorganic particles and the binder in a solvent; and (d) coating the slurry on at least one surface of the porous support and drying it to form an inorganic coating layer.

Description

Manufacturing method of inorganic coating separator {A METHOD FOR MANUFACTURING A SEPARATOR COATED WITH INORGANIC MATERIALS}

The present invention relates to a method for manufacturing an inorganic coating separator.

Lithium secondary batteries are widely used as a power source for various electric products that require miniaturization and weight reduction, such as smartphones, laptops, and tablet PCs. The development of a lithium secondary battery having a large size, long lifespan, and high stability is required.

As a means for achieving the above object, a separator with micropores that separates the positive electrode and the negative electrode to prevent an internal short and facilitates the movement of lithium ions during charging and discharging, in particular, thermally induced phase separation (Thermally Induced Phase Separation) R&D on microporous membranes using polyolefins such as polyethylene, which is advantageous for pore formation, economical, and easy to meet the physical properties required for membranes.

However, a separator using polyethylene having a low melting point of about 135° C. may undergo shrinkage deformation at a high temperature higher than the melting point due to heat generation of the battery. When a short circuit occurs due to such deformation, a thermal runaway phenomenon of the battery may occur, resulting in safety problems such as ignition. In order to solve this problem, a method of improving heat resistance by coating ceramic particles on the surface of a separator or crosslinking a polyolefin separator has been proposed.

Japanese Patent No. 4583532 discloses a method for manufacturing a separator by mixing ultra-high molecular weight polyethylene with a weight average molecular weight of 500,000 or more with silane-modified polyolefin, but the ultra-high molecular weight polyethylene has poor dispersibility with the silane-modified polyolefin. have. Accordingly, the prepared separation membrane has a high waste rate, and the silane cross-linkable polyolefin is concentrated in some areas, so that a separation membrane with uniform physical properties cannot be obtained.

It is reported that the ceramic coated separator has significantly improved heat resistance compared to the separator without a ceramic coating layer. However, these ceramic-coated separators leave significant technical challenges with respect to air permeability, which is a factor that has a very important effect on the performance of the separator. That is, when the ceramic coating layer is formed on the surface of the porous substrate, the heat resistance of the separator is improved, but the coating layer closes the pores formed on the porous substrate, thereby reducing the air permeability of the separator, and thus the ion movement path between the anode and the cathode is greatly increased As a result, the charging and discharging performance of the secondary battery is greatly deteriorated.

In addition, Korea Patent No. 1955911 discloses that the time required for the hydro-crosslinking of the polyolefin membrane can be reduced to a minimum of about 10 hours by using a crosslinking catalyst, etc., but it is difficult to sufficiently secure productivity with such a crosslinking time, Korean Patent Application Laid-Open No. 10-2020-0061575 discloses that heat resistance can be further improved by coating ceramic particles on the surface of the polyolefin separator according to Korean Patent No. 1955911, but the coating process is not improved while the crosslinking rate is not improved. There is a problem in that productivity is further reduced as it is added.

The present invention is to solve the problems of the prior art described above, and an object of the present invention is to provide a method for manufacturing a separator capable of improving the productivity of a porous separator having a structure crosslinked by moisture and a heat-resistant coating layer.

One aspect of the present invention, (a) manufacturing a porous support by processing a composition comprising a first polyolefin and a second polyolefin modified with a crosslinking compound; (b) applying steam to the porous support to crosslink the second polyolefin included in the porous support; (c) preparing a slurry by dissolving the inorganic particles and the binder in a solvent; and (d) coating the slurry on at least one surface of the porous support and drying it to form an inorganic coating layer.

In an embodiment, the weight average molecular weight (Mw) of the first polyolefin may be 250,000 to 450,000 g/mol, and the molecular weight distribution (Mw/Mn) may be 3 to 7.

In one embodiment, the first and second polyolefins are polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof, respectively. It may include one selected from the group consisting of.

In one embodiment, the crosslinkable compound may be a hydrocarbon-based compound including one or more alkoxy groups and one or more vinyl groups, a silane-based compound, or a combination thereof.

In one embodiment, the content of the crosslinkable compound in the second polyolefin may be 1 to 50% by weight.

In one embodiment, the composition further includes a crosslinking catalyst, and the content of the crosslinking catalyst in the composition may be 0.01 to 10% by weight.

In one embodiment, in step (b), the steam is applied in an amount of 0.1-5 kg/m ² for 10 minutes to 1 hour to adjust the gel fraction of the porous support to 60% or more.

In one embodiment, in step (b), before steam is applied to the porous support, the porous support may be coated with a solution containing a crosslinking catalyst, and the content of the crosslinking catalyst in the solution is 0.01 to 10 % by weight.

In one embodiment, the first and second polyolefins in the product of step (b) constitute a continuous phase and a discontinuous phase, respectively, and the content of the second polyolefin in the product of step (b) is 0.1 to 90 % by weight.

In one embodiment, the inorganic particles are SiO ₂ , AlO(OH), Mg(OH) ₂ , Al(OH) ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , Al ₂ O ₃ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO ₆ and combinations of two or more thereof; The solvent is methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, distilled water and It may be one selected from the group consisting of a combination of two or more of these, and the binder is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate , polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl Polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose, cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer , styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer, polyethylene glycol, acrylic rubber, and may be one selected from the group consisting of combinations of two or more thereof.

In the method for manufacturing a separator according to an aspect of the present invention, the time required for crosslinking of the porous support can be significantly reduced by crosslinking the second polyolefin modified with a crosslinkable compound dispersed in the porous support using steam, This contributes to shortening the time required for the entire process including the crosslinking of the porous support and the ceramic coating, thereby improving the productivity of the separator.

It should be understood that the effects of the present invention are not limited to the above-described effects, and include all effects that can be inferred from the configuration of the invention described in the detailed description or claims of the present invention.

Hereinafter, the present invention will be described. However, the present invention may be embodied in several different forms, and thus is not limited to the embodiments described herein.

Throughout the specification, when a part is "connected" with another part, this includes not only the case of being "directly connected" but also the case of being "indirectly connected" with another member interposed therebetween. . In addition, when a part "includes" a certain component, this means that other components may be further provided without excluding other components unless otherwise stated.

One aspect of the present invention, (a) manufacturing a porous support by processing a composition comprising a first polyolefin and a second polyolefin modified with a crosslinking compound; (b) applying steam to the porous support to crosslink the second polyolefin included in the porous support; (c) preparing a slurry by dissolving the inorganic particles and the binder in a solvent; and (d) coating the slurry on at least one surface of the porous support and drying it to form an inorganic coating layer.

In step (a), the weight average molecular weight (Mw) is 250,000 ~ 450,000 g / mol, the molecular weight distribution (Mw / Mn) is 3 to 7 of the first polyolefin and the second polyolefin modified with a crosslinking compound comprising After putting the composition in the extruder, extruding it, discharging it through a T-die, forming a sheet, and then stretching, extracting and removing the pore former included in the composition to prepare a porous support.

The porous support may be a type of porous membrane, in which pores are formed. In the porous support, the second polyolefin may be crosslinked in a continuous matrix including the first polyolefin to firmly support and fix the matrix, thereby improving mechanical properties and heat resistance of the porous support.

As used herein, the term “matrix” refers to a component constituting a continuous phase in a system including two or more components. That is, in the porous support, the first polyolefin having a weight average molecular weight (M _w ) of 250,000 to 450,000 g/mol and a molecular weight distribution (Mw/Mn) of 3 to 7 exists in a continuous phase, and the cross-linked agent therein 2 The polyolefin may be uniformly dispersed in a discontinuous phase.

It is necessary to control the distribution of the second polyolefin to be uniformly distributed so that the crosslinked second polyolefin is uniformly distributed in the porous support. When the crosslinking reaction of the second polyolefin is biased in some regions of the porous support, the required level of mechanical properties cannot be realized. can be significantly lowered.

By adjusting the molecular weight of the first polyolefin constituting the matrix to a certain range, the second polyolefin may be uniformly dispersed in the first polyolefin while the first and second polyolefins are kneaded in the extruder. The weight average molecular weight (M _w ) of the first polyolefin may be 250,000 to 450,000 g/mol. If the weight average molecular weight of the first polyolefin exceeds 450,000 g/mol, the viscosity may increase and processability may decrease, and if it is less than 250,000 g/mol, the viscosity becomes excessively low and the dispersibility of the second polyolefin is extremely reduced. Accordingly, phase separation or layer separation may occur between the first and second polyolefins. In addition, the first polyolefin molecular weight distribution (Mw/Mn) may be 3-7. If the molecular weight distribution of the first polyolefin is less than 3, the dispersibility with the second polyolefin and the pore former may be lowered, so that the uniformity of the prepared separator may decrease, and if it exceeds 7, the mechanical strength of the final separator may decrease. have.

The first and second polyolefins are each selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. may be, and preferably, polyethylene, but is not limited thereto.

The composition may include 20 to 40 parts by weight of the first polyolefin and 0.1 to 20 parts by weight of the second polyolefin. If the content of the second polyolefin in the composition is less than 0.1 parts by weight, the required level of mechanical properties cannot be implemented, and if it exceeds 20 parts by weight, the elongation of the porous support is reduced and other mechanical properties converge to the required level. It is disadvantageous in terms of economy and productivity.

The second polyolefin may be a polyolefin grafted with a crosslinkable compound, and the content of the crosslinkable compound in the second polyolefin may be 1 to 50% by weight. If the content of the crosslinkable compound in the second polyolefin is less than 1% by weight, the crosslinking reaction is inhibited and it is difficult to improve the mechanical properties and heat resistance of the porous support and the separator including the same, and if it is more than 50% by weight, the elongation of the porous support is Not only does it decrease, but other mechanical properties converge to the required level, which is disadvantageous in terms of economy and productivity.

The crosslinkable compound may be a hydrocarbon-based compound including at least one alkoxy group and at least one vinyl group, a silane-based compound, or a combination thereof.

The silane-based compound may be a vinylsilane containing an alkoxy group. For example, the vinylsilane containing the alkoxy group may be one selected from the group consisting of trimethoxyvinylsilane, triethoxyvinylsilane, triacetoxyvinylsilane, and combinations of two or more thereof, preferably, It may be methoxyvinylsilane, but is not limited thereto.

However, since the boiling point of the silane-based compound is in the range of about 120 to 180° C., a difference between the input amount and the actual amount participating in the reaction occurs because it is volatilized in a process of 180° C. or higher, for example, an extrusion process. The difference in the actual amount of reaction participation compared to the input amount of the silane-based compound may negatively affect reproducibility, mass productivity, and quality in the subsequent crosslinking of the porous support.

In contrast, by using the second polyolefin grafted with a hydrocarbon-based compound containing at least one alkoxy group and at least one vinyl group having a relatively high boiling point, kneadability with the raw material is improved, and the low boiling point material is volatilized and generated during extrusion. It is possible to improve the productivity of the separation membrane by preventing the die drool phenomenon.

The hydrocarbon-based compound may be grafted to the second polyolefin by a vinyl group, and may undergo a crosslinking reaction by an alkoxy group to crosslink the second polyolefin.

The boiling point of the hydrocarbon-based compound may be 160 °C or higher, preferably 160 to 300 °C, more preferably 170 to 250 °C. When the boiling point of the hydrocarbon-based compound has the above range, the die drool phenomenon can be prevented, and the solvent can be easily reused by reducing the content of impurities in the solvent from which the pore former is extracted, for example, dichloromethane.

The hydrocarbon-based compound is, for example, 3,3,3-triethoxy-1-propene (3,3,3-trimethoxy-1-propene), (2E)-1,1,4,4- Tetramethoxy-2-butene ((2E)-1,1,4,4-tetramethoxy-2-butene), 2-(2-(2-methoxyethoxy)ethoxy)ethyl acrylate (2-( 2-(2-methoxyethoxy)ethoxy)ethylacrylate), 2-(2-ethoxy)ethoxy)ethylacrylate (2-(2-(2-ethoxyethoxy)ethylacrylate), dimethyl fumarate, (2E) )-4,4-dimethoxy-2-butenal ((2E)-4,4-dimethoxy-2-butenal), 2-methoxyethyl methacrylate, and combinations of two or more thereof It may be one selected from the group consisting of, but is not limited thereto.

The composition may further include 60 to 80 parts by weight of a pore former. The pore former may be extracted and removed from the inside of the support by a wet method using thermally induced phase separation to form pores.

In the wet method, the support including the pore-forming agent may be immersed in an extraction tank in which a solvent is supported. The extraction temperature may be 15 ~ 80 ℃, preferably 25 ~ 40 ℃, the extraction time may be 0.1 ~ 60 minutes, preferably 1 ~ 20 minutes.

The pore-forming agent is, for example, paraffin oil, paraffin wax, mineral oil, solid paraffin, soybean oil, rapeseed oil, palm oil, palm oil, di-2-ethylhexyl phthalate, dibutyl phthalate, diisononyl phthalate, diisodecyl phthalate , may be one selected from the group consisting of bis(2-propylheptyl)phthalate, naphthenoyl, and a combination of two or more thereof, preferably paraffin oil, and more preferably, a kinematic viscosity of 50~ It may be 100 cSt paraffin oil, but is not limited thereto.

The solvent for extracting the pore former may be one selected from the group consisting of pentane, hexane, benzene, dichloromethane, carbon tetrachloride, methyl ethyl ketone, acetone, and a combination of two or more thereof, preferably, dichloromethane However, the present invention is not limited thereto.

The composition may further include a crosslinking catalyst, and the content of the crosslinking catalyst in the composition may be 0.01 to 10% by weight. The crosslinking catalyst may accelerate a crosslinking reaction between alkoxy groups contained in the crosslinkable compound grafted to the second polyethylene, thereby shortening the crosslinking time.

The crosslinking catalyst may be one selected from the group consisting of carboxylate salts of metals such as tin, zinc, iron, lead, cobalt, organic bases, inorganic acids, organic acids, and combinations of two or more thereof, but is not limited thereto.

The carboxylate salt of the metal is, for example, dibutyltindilaurate, dibutyltindiacetate, stannous acetate, stannous caprylic acid, zinc naphthenate, caprylic acid as the carboxylate salt of the metal. zinc, cobalt naphthenate, or the like. The organic base may be, for example, ethylamine, dibutylamine, hexylamine, pyridine, or the like. The inorganic acid may be, for example, sulfuric acid or hydrochloric acid, and the organic acid may be, for example, toluene sulfonic acid, acetic acid, stearic acid, maleic acid, and the like.

The content of the crosslinking catalyst in the composition may be 0.01 to 10% by weight. When the content of the crosslinking catalyst in the composition has the above range, a crosslinking reaction at a required level may be induced, any side reactions may not occur in the battery, and problems such as wasted crosslinking catalyst do not occur.

The stretching performed in step (a) may be performed by a known method such as uniaxial stretching or biaxial stretching (sequential or simultaneous biaxial stretching). In the case of sequential biaxial stretching, the draw ratio may be 4 to 20 times in the transverse direction (MD) and the longitudinal direction (TD), respectively, and the plane magnification accordingly may be 16 to 400 times.

In step (b), steam may be applied to the porous support to crosslink the second polyolefin included in the porous support. As used herein, the term “steam” refers to water vapor or superheated water vapor generated by heating liquid water to a boiling point (100° C.) or higher.

In the case of crosslinking the porous support and/or the separation membrane into which the crosslinkable compound is introduced using conventional moisture, the required level of crosslinking, for example, about 60% or higher, is placed in a thermo-hygrostat for 12 hours at less than 100° C. Above, preferably, since it should be left for at least 24 hours, the process for manufacturing the porous support and/or the separation membrane is stagnated by this crosslinking process, thereby significantly reducing productivity.

In step (b), the time required for crosslinking of the porous support can be significantly shortened by adopting a more active method of applying a certain amount of steam to the porous support, instead of leaving the porous support in a constant temperature and humidity bath. have.

That is, in step (b), by using a certain amount of steam to cross-link the second polyolefin in the porous support, the same level of cross-linking within a short time compared to the conventional method of leaving it in a constant temperature and humidity chamber, and the resulting mechanical Physical properties and heat resistance can be realized. In addition, the shortening of the crosslinking time contributes to shortening the time required for the entire process including the crosslinking of the porous support and subsequent ceramic coating, thereby improving the productivity of the separator.

The steam is applied in an amount of 0.1 to 5 kg/m ² , preferably 1 to 3 kg/m ² for 10 minutes to 1 hour, preferably, 20 minutes to 50 minutes to increase the gel fraction of the porous support by 60% or more can be adjusted with If the amount of steam is less than 0.1kg/m ² or the time the steam is applied is less than 10 minutes, the required level of mechanical properties and heat resistance cannot be implemented, and if the amount of steam is more than 5kg/m ² or the steam If the time applied is more than 1 hour, the elongation of the porous support is lowered, and other mechanical properties converge to a required level, which is disadvantageous in terms of economic efficiency and productivity.

In step (b), before steam is applied to the porous support, the porous support from which the pore former is extracted and removed may be coated or impregnated with a solution containing a crosslinking catalyst. The application may be performed by one method selected from the group consisting of roll coating, bar coating, spray coating, dip coating, die coating, comma coating, and a combination of two or more thereof.

The solution may include a crosslinking catalyst, and the content of the crosslinking catalyst in the solution may be 0.01 to 10% by weight. The crosslinking catalyst may be introduced to both surfaces of the porous support and the surfaces of the internal pores in the same manner as described above to promote a crosslinking reaction between the alkoxy groups contained in the crosslinkable compound, thereby further shortening the crosslinking time.

The crosslinking catalyst may be one selected from the group consisting of carboxylate salts of metals such as tin, zinc, iron, lead, cobalt, organic bases, inorganic acids, organic acids, and combinations of two or more thereof, but is not limited thereto.

The carboxylate salt of the metal is, for example, dibutyltindilaurate, dibutyltindiacetate, stannous acetate, stannous caprylic acid, zinc naphthenate, caprylic acid as the carboxylate salt of the metal. zinc, cobalt naphthenate, or the like. The organic base may be, for example, ethylamine, dibutylamine, hexylamine, pyridine, or the like. The inorganic acid may be, for example, sulfuric acid or hydrochloric acid, and the organic acid may be, for example, toluene sulfonic acid, acetic acid, stearic acid, maleic acid, and the like.

The content of the crosslinking catalyst in the solution may be 0.01 to 10% by weight. When the content of the cross-linking catalyst in the solution is within the above range, a cross-linking reaction at a required level may be induced, any side reactions may not occur in the battery, and problems such as wasting of the cross-linking catalyst do not occur.

The first and second polyolefins in the product of step (b) constitute a continuous phase and a discontinuous phase, respectively, and the content of the second polyolefin in the product of step (b) may be 0.1 to 90% by weight.

The product of step (b) may be a type of porous membrane, in which pores are formed. In the product of step (b), the second polyolefin is crosslinked in a continuous matrix including the first polyolefin to firmly support and fix the matrix, thereby improving the mechanical properties and heat resistance of the porous support.

As used herein, the term “matrix” refers to a component constituting a continuous phase in a system including two or more components. That is, in the porous support, the first polyolefin having a weight average molecular weight (M _w ) of 250,000 to 450,000 g/mol and a molecular weight distribution (Mw/Mn) of 3 to 7 exists in a continuous phase, and the cross-linked agent therein 2 The polyolefin may be uniformly dispersed in a discontinuous phase.

The content of the second polyolefin in the product of step (b) may be 0.1 to 90% by weight, preferably, 0.1 to 50% by weight, more preferably, 0.1 to 30% by weight. If the content of the second polyolefin in the product of step (b) is less than 0.1% by weight, the required level of mechanical properties and heat resistance cannot be realized, and if it exceeds 90% by weight, the elongation of the porous support is reduced as well as other mechanical properties. Since the physical properties converge to the required level, it is disadvantageous in terms of economy and productivity.

The porous support prepared through step (b) may satisfy one or more of the following conditions (i) to (ix). (i) air permeability 125~300sec/100ml; (ii) 200-400 gf of puncture strength; (iii) longitudinal (MD) tensile strength 1,500~3,000kgf/cm ² ; (iv) Transverse direction (TD) tensile strength 1,000~2,500kgf/cm ² ; (v) longitudinal (MD) tensile elongation of 50 to 150%; (vi) 50-100% transverse (TD) tensile elongation; (vii) 10% or less of longitudinal heat shrinkage at 120°C; (viii) 15% or less of transverse heat shrinkage at 120°C; (ix) Meltdown temperature 200~250℃.

In step (c), the inorganic particles and the binder may be dissolved in a solvent to prepare a slurry. The slurry may contain 30 to 100 parts by weight of inorganic particles and 1 to 20 parts by weight of a binder based on 100 parts by weight of the solvent, and preferably, may be water-soluble (aqueous or water-based). The content of solids in the slurry may be adjusted to 20 to 50% by weight, preferably 30 to 40% by weight, in consideration of the balance between processability, workability, and heat resistance. In addition, the slurry may further include a certain amount of a dispersant, for example, 0.01 to 0.5 parts by weight of sodium hexametaphosphate.

The inorganic particles are SiO ₂ , AlO(OH), Mg(OH) ₂ , Al(OH) ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , Al ₂ O ₃ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO ₆ and one selected from the group consisting of a combination of two or more thereof, preferably boehmite (AlO(OH) ), but is not limited thereto.

When the inorganic particles are plate-shaped AlO(OH), the surface portion of the AlO(OH) particle has a (-) charge and the edge portion has a (+) charge, so the surface portion and the edge portion of the AlO(OH) particle adjacent to each other have a (+) charge. The particles tend to agglomerate by binding by electrostatic attraction. Aggregation of such inorganic particles may impair the uniformity of physical properties on the surface of the separation membrane. In contrast, the inorganic coating layer may further include an additive for improving the dispersibility of the inorganic particles, for example, a dispersant, a surfactant, and the like. In particular, the inorganic coating layer may include sodium hexametaphosphate ((NaPO ₃ ) ₆ ) as a dispersing agent, and the content of the sodium hexametaphosphate in the inorganic coating layer is 0.01 to 1% by weight, preferably, 0.01 to 0.5 % by weight. The sodium hexametaphosphate is adsorbed to the edge of the AlO(OH) particles to weaken the negative charge of the edge, effectively preventing the AlO(OH) particles from aggregating, and the slurry for forming the inorganic coating layer In addition to the storage stability of the inorganic coating layer, it is possible to improve the dispersibility of the inorganic particles.

The binder is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate , Ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose , cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer It may be one selected from the group consisting of a copolymer, polyethylene glycol, acrylic rubber, and a combination of two or more thereof, and preferably, carboxymethyl cellulose and an alkyl acrylate-acrylonitrile copolymer, but is not limited thereto. For example, in the inorganic coating layer, the carboxymethyl cellulose and the alkyl acrylate-acrylonitrile copolymer may be present in a weight ratio of 1: 0.5 to 1.5, respectively.

The content of the inorganic particles in the inorganic coating layer may be 50 to 95% by weight. If the content of the inorganic particles in the inorganic coating layer is less than 50% by weight, the required level of heat resistance cannot be imparted. .

The inorganic coating layer may have a thickness of 1 to 10 μm. If the thickness of the inorganic coating layer is less than 1 μm, a required level of heat resistance cannot be imparted, and when it exceeds 10 μm, the separator is thickened, thereby inhibiting the miniaturization and integration of batteries or devices.

The slurry may contain 30 to 100 parts by weight of inorganic particles and 1 to 20 parts by weight of a binder based on 100 parts by weight of the solvent, and preferably, may be water-soluble (aqueous or water-based). The content of solids in the slurry may be adjusted to 20 to 50% by weight, preferably 30 to 40% by weight, in consideration of the balance between processability, workability, and heat resistance. In addition, the slurry may further include a certain amount of a dispersant, for example, 0.01 to 0.5 parts by weight of sodium hexametaphosphate.

To prepare the aqueous slurry, the solvent is methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid , dimethyl sulfoxide, distilled water, and may be one selected from the group consisting of a combination of two or more thereof, preferably, ethanol and water, more preferably, ethanol and water are each mixed in a weight ratio of 1: 10-50 may be, but is not limited thereto.

In step (d), at least one surface, preferably, both surfaces of the porous support may be coated with the slurry and dried to form an inorganic coating layer. The inorganic coating layer may be formed on at least one surface of the porous support, and if necessary, may be impregnated into at least some of the pores in the porous support.

The coating is a batch coating of the slurry prepared in step (c) in one method selected from the group consisting of roll coating, bar coating, spray coating, dip coating, die coating, comma coating, and a combination of two or more thereof. Drying may be carried out in a manner to collectively remove the solvent and other liquid residues contained in the slurry.

In addition, the coating may be made by phase separation. The slurry may include inorganic particles and a binder, and the binder may be a gel polymer. In addition, it may be understood that the inorganic particles do not substantially affect the phase separation since they are not dissolved in a solvent serving as a dispersion medium in the slurry.

In the separation membrane having an inorganic coating layer including a plurality of open three-dimensional pores connected to each other on the porous support, when a non-solvent is added to the gel polymer solution, a part of the solvent is substituted with the non-solvent, so that the gel polymer-rich phase and the gel It can be prepared using phase separation into a polymer-deficient phase.

When pores are formed in a gel polymer using a plasticizer as disclosed in US Patent No. 5,460,904, the position of the plasticizer for forming pores is not flexible, so that closed pores are formed. On the other hand, the present invention relates to a phase separation of a solvent/non-solvent phase, that is, a liquid-liquid phase separation phenomenon into a gel polymer-rich phase and a gel polymer-depleted phase, and a liquid phase gel polymer-deficient phase to form pores. Since the (phase) is fluid and pore growth is possible by excess Gibbs free energy, it is possible to provide an inorganic coating layer having a three-dimensional open-porous structure in which pores are connected.

The phase separation of the solvent/non-solvent is caused during the preparation of the gel polymer solution, the coating of the gel polymer, and/or the drying, so that the gel polymer-deficient phase that will form the pores is formed three-dimensionally and connected to each other. can do. In addition, in order to form the open three-dimensional pores, drying conditions, types and contents of the solvent and non-solvent may be adjusted.

First, a slurry obtained by adding a non-solvent to a solution in which a gel polymer and inorganic particles are dissolved in a solvent is applied to a porous support and dried at a temperature of 50 to 130° C. An inorganic coating layer including dimensional pores may be formed. However, in this case, the slurry itself is phase-separated and long-term storage stability is lowered, so it may not be suitable for mass production.

Alternatively, a slurry obtained by dissolving a gel polymer and inorganic particles in a solvent is applied on a porous support and then immersed in a non-solvent to apply phase separation, dried at a temperature of 50 to 130° C., and connected to each other on the porous support. An inorganic coating layer including pores may be formed. However, in this case, since phase separation occurs during immersion in the non-solvent and the solvent is mixed with the non-solvent, the composition of the non-solvent is changed, thereby making it difficult to form pores having a uniform shape.

Alternatively, a slurry in which a gel polymer and inorganic particles are dissolved in a solvent is applied on a porous support, and phase-separated by spraying a non-solvent vapor when drying at a temperature of 50 to 130° C. It is possible to form an inorganic coating layer comprising a. In this case, since the slurry in a stable form is applied to the porous support and non-solvent vapor is sprayed during drying, open three-dimensional pores having a uniform form can be formed.

The gel polymer is preferably a polymer having a solubility index of 15 to 45 MPa ^1/2 . If the solubility index is less than 15 MPa ^1/2 or more than 45 MPa ^1/2 , this is because it is difficult to be impregnated by a conventional liquid electrolyte for batteries. Therefore, it is advantageous that the gel polymer is a hydrophilic polymer having more polar groups than hydrophobic polymers such as polyolefins.

The gel polymer may have a glass transition temperature (Tg) as low as possible, and is preferably in the range of -200 to 200°C. This is because mechanical properties such as flexibility and elasticity of the gel polymer layer can be improved.

As a solvent for dissolving the gel polymer, it is preferable that the gel polymer to be used has a solubility index similar to that of the gel polymer and has a low boiling point. This is to facilitate uniform mixing and subsequent solvent removal.

Non-limiting examples of the solvent that can be used include acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (N -methyl-2-pyrrolidone, NMP), cyclohexane, or a mixture thereof. In addition, non-limiting examples of the non-solvent for the gel polymer include alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, and butyl alcohol, and water.

On the other hand, the molecular weight of the gel polymer is suitable between 10,000 and 1,000,000. If the molecular weight is excessively low, it is difficult to form a uniform inorganic coating layer during coating. If the molecular weight is high, the solubility in solvent decreases and the viscosity increases excessively. there are difficulties in

The appropriate concentration of the gel polymer to the solvent is 0.1 to 30%. If the concentration of the polymer is excessively low, it is difficult to form a uniform inorganic coating layer. If the concentration of the polymer is excessively high, it is not well soluble in the solvent and is There is a difficulty in the process due to the increase in viscosity.

The ratio of the non-solvent to the solvent is appropriate in the range of 0.1 to 50% by volume. If the non-solvent ratio is excessively low, phase separation does not occur. happens to be

A method of coating the gel polymer solution or the gel polymer solution containing a non-solvent on the porous support may use a conventional method known in the art, for example, roll coating, bar coating, spray coating, dip coating, One method selected from the group consisting of die coating, comma coating, and a combination of two or more thereof may be used. In addition, at the time of coating, it may be carried out on both sides of the porous support, or it may be selectively carried out on only one surface.

In order to form an inorganic coating layer including a plurality of open three-dimensional pores connected to each other, it is preferable to adjust the drying temperature to 50 to 130°C. If the drying temperature is excessively low, the solvent and nonsolvent may remain, which may cause problems in battery performance, and if it exceeds 130° C., the porous support may be damaged. The drying time is suitable between 5 seconds and 250 seconds.

As such, when forming pores from the gel polymer-deficient phase, the size and porosity of pores, whether pores are connected, etc. can be controlled by the selection/content ratio of solvent/non-solvent, drying temperature/time, and the like. In order to increase the size of the pores and increase the connection between the pores, the drying temperature is lowered and the drying time is increased to sufficiently grow the phase-separated gel polymer-deficient phase. The average pore size of the open three-dimensional pores may be 0.01 to 10㎛.

Meanwhile, in step (d), before coating the slurry on at least one surface of the porous support, the porous support may be plasma-treated in the presence of a mixed gas containing sulfur dioxide (SO ₂ ) and oxygen (O ₂ ). have.

By making the surface of the porous support and/or the surface of the internal pores hydrophilic through the plasma treatment, the bonding force between the porous support and the slurry can be improved, thereby significantly improving the durability of the separator, in particular, long-term durability and heat resistance. can be improved

Conventionally, in order to hydrophilize the surface of a porous support, a wet process in which the support is sulfonated by immersing the support in sulfuric acid for a certain period of time has been mainly used, but in this case, the wet process is preceded or followed by the plasma treatment. Since it is performed separately, the process is complicated, and there is a problem in that a large amount of process waste liquid is generated.

In contrast, since the process gas used in the plasma treatment includes a certain amount of sulfur dioxide gas as well as the conventional air, oxygen and/or inert gas, the plasma treatment is a single process without a wet process such as immersing the porous support in sulfuric acid or the like. By creating a functional group such as -SO ₃ on the surface of the porous support and the surface of the internal pores through the dry process of It can simplify the complicated process of

The mixed gas, which is a process gas used in the plasma treatment, is 50 to 90 vol% of sulfur dioxide and 10 to 50 vol% of oxygen, preferably 60 to 80 vol% of sulfur dioxide and 20 to 40 vol% of oxygen, more preferably, It may contain 70 to 80% by volume of sulfur dioxide and 20 to 30% by volume of oxygen. If the content of sulfur dioxide in the mixed gas is less than 50% by volume, the hydrophilicity required for the porous support may not be implemented, and if it exceeds 90% by volume, the process may be unstable.

The plasma treatment may be performed for 0.5 to 90 minutes, preferably, 0.5 to 20 minutes. When the plasma treatment is performed for less than 0.5 minutes, the porous support cannot be hydrophilized or sulfonated to the required level, and when it is performed for more than 90 minutes, the hydrophilicity and sulfonation degree converge to a certain level, thereby reducing process efficiency. .

On the other hand, the meltdown temperature of the separator prepared through step (d) may be 220 °C or higher, preferably 230 to 300 °C.

Hereinafter, embodiments of the present invention will be described in detail.

Example 1

29.5 parts by weight of high-density polyethylene having a weight average molecular weight (M _w ) of 350,000, MFR 0.8 g/10 min, 0.5 parts by weight of trimethoxyvinylsilane-modified high-density polyethylene having a density of 0.958 g/ml, and paraffin having a kinematic viscosity of 70 cSt at 40°C 70 parts by weight of oil was mixed and put into a twin screw extruder (inner diameter 58mm, L/D=56, twin screw extruder). After discharging from the twin-screw extruder to a T-die having a width of 300 mm under the conditions of 200° C. and a screw rotation speed of 40 rpm, a base sheet having a thickness of 800 μm was prepared by passing through a casting roll having a temperature of 40° C. A stretched film was prepared by stretching the base sheet 6 times in the longitudinal direction (MD) in a roll stretching machine at 110° C., and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 125° C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 50° C. for 5 minutes. Thereafter, after heating to 125° C. in a tenter stretching machine, it was stretched 1.45 times in the transverse direction (TD) and then relaxed 1.25 times. Steam was applied to both sides of the film in an amount of 2 kg/m ² for 50 minutes to prepare a porous support having a thickness of 9.4 μm.

Carboxymethylcellulose salt (CMC), acryl-acrylonitrile copolymer latex, boehmite (AlO(OH)), dispersant ((NaPO ₃ ) ₆ ), surfactant, water, and ethanol were mixed in the ratio of Table 1 below. Then, it was dispersed with a ball-mill to prepare an aqueous dispersion ceramic slurry.

division Input (g) Solid content (g) Solid content (%) Dry content (%) water 1,500 0 0 0 ethanol 70 0 0 0 CMC 27 27 100 3.3 Acrylic-acrylonitrile copolymer latex 70 31.5 45 3.9 bohemite 750 750 100 92.4 (NaPO ₃ ) ₆ 1.5 1.5 100 0.2 Surfactants 2 2 100 0.2 Sum 2,421 812 - 100

The aqueous dispersion ceramic slurry is coated on both sides of the porous support, gravure coated with a roll of 110 mesh, and dried in a hot air oven at a temperature of 80° C. for 1 hour. An inorganic coating layer having a thickness of 2 μm on both sides of the porous support. The formed separation membrane was prepared.

Example 2

29.5 parts by weight of high-density polyethylene having a weight average molecular weight (M _w ) of 350,000, MFR 0.8 g/10 min, 0.5 parts by weight of trimethoxyvinylsilane-modified high-density polyethylene having a density of 0.958 g/ml, and paraffin having a kinematic viscosity of 70 cSt at 40°C 70 parts by weight of oil was mixed and put into a twin screw extruder (inner diameter 58mm, L/D=56, twin screw extruder). Dibutyltin dilaurate, a crosslinking catalyst, was pre-dispersed in some of the paraffin oil, and added through the side feeder of the twin-screw extruder so as to be 0.01 wt% based on the total weight of the material passing through the twin-screw extruder. After discharging from the twin-screw extruder to a T-die having a width of 300 mm under the conditions of 200° C. and a screw rotation speed of 40 rpm, a base sheet having a thickness of 800 μm was prepared by passing through a casting roll having a temperature of 40° C. A stretched film was prepared by stretching the base sheet 6 times in the longitudinal direction (MD) in a roll stretching machine at 110° C., and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 125° C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute. The film from which the paraffin oil was removed was dried at 50° C. for 5 minutes. Thereafter, after heating to 125° C. in a tenter stretching machine, it was stretched 1.45 times in the transverse direction (TD) and then relaxed 1.25 times. Steam was applied to both sides of the film in an amount of 2 kg/m ² for 30 minutes to prepare a porous support having a thickness of 9.6 μm.

Other than that, a separation membrane was prepared in the same manner as in Example 1.

Example 3

29.5 parts by weight of high-density polyethylene having a weight average molecular weight (M _w ) of 350,000, MFR 0.8 g/10 min, 0.5 parts by weight of trimethoxyvinylsilane-modified high-density polyethylene having a density of 0.958 g/ml, and paraffin having a kinematic viscosity of 70 cSt at 40°C 70 parts by weight of oil was mixed and put into a twin screw extruder (inner diameter 58mm, L/D=56, twin screw extruder). After discharging from the twin-screw extruder to a T-die having a width of 300 mm under the conditions of 200° C. and a screw rotation speed of 40 rpm, a base sheet having a thickness of 800 μm was prepared by passing through a casting roll having a temperature of 40° C. A stretched film was prepared by stretching the base sheet 6 times in the longitudinal direction (MD) in a roll stretching machine at 110° C., and stretching 7 times in the transverse direction (TD) in a tenter stretching machine at 125° C. The stretched film was impregnated in a dichloromethane leaching tank at 25° C. to extract and remove paraffin oil for 1 minute, and the concentration of dibutyltindilaurate, a crosslinking catalyst, was adjusted to 1% by weight. Then, it was dried at 50 °C for 5 minutes. Thereafter, after heating to 125° C. in a tenter stretching machine, it was stretched 1.45 times in the transverse direction (TD) and then relaxed 1.25 times. Steam was applied to both sides of the film in an amount of 2 kg/m ² for 20 minutes to prepare a porous support having a thickness of 9.4 μm.

Other than that, a separation membrane was prepared in the same manner as in Example 1.

Comparative Example 1

Instead of applying steam to both sides of the film in an amount of 2 kg / m ² for 50 minutes, the film was crosslinked for 72 hours in a thermo-hygrostat at 85 ° C. and 85% humidity to prepare a porous support. A separation membrane was prepared in the same manner as in Example 1.

Comparative Example 2

Instead of applying steam to both sides of the film in an amount of 2 kg/m ² for 30 minutes, the film was cross-linked in a thermo-hygrostat at 85° C. and humidity of 85% for 60 hours to prepare a porous support. A separation membrane was prepared in the same manner as in Example 2.

Comparative Example 3

Instead of applying steam to both sides of the film in an amount of 2 kg/m ² for 20 minutes, the film was cross-linked in a thermo-hygrostat at 85° C. and humidity of 85% for 24 hours to prepare a porous support. A separation membrane was prepared in the same manner as in Example 2.

Comparative Example 4

A separator was prepared in the same manner as in Example 1, except that steam was applied for 5 minutes instead of steam for 50 minutes of the film.

Comparative Example 5

Instead of applying steam in an amount of 2 kg/m ² to both sides of the film, a separator was prepared in the same manner as in Example 1, except that steam was applied in an amount of 0.08 kg/m ² .

Experimental example

The test method for the physical properties of the porous support and the membrane specimen measured in the present invention is as follows. Unless otherwise stated, the temperature was measured at room temperature (25° C.).

-Tensile strength (kgf/cm ² ): Using a tensile strength measuring device, stress was applied to a porous support specimen having a size of 20 × 200 mm in the transverse (TD) and longitudinal (MD) directions, and the applied stress was measured until fracture occurred. .

-Tensile Elongation (%): Measure the maximum length that is stretched until fracture occurs by applying stress in the transverse (TD) and longitudinal (MD) directions to a porous support specimen having a size of 20 × 200 mm using a tensile strength measuring instrument, and the following formula was used to calculate the tensile elongation.

(In the above formula, l ₁ is the transverse or longitudinal length of the porous support specimen before stretching, and l ₂ is the transverse or longitudinal length of the porous support specimen immediately before fracture.)

-Heat shrinkage (%): After placing a 200 × 200 mm porous support specimen in an oven at 120 ° C. for 1 hour between A4 paper and leaving it to stand, it was cooled to room temperature to measure the width (TD) and length (MD) of the specimen. The contracted length was measured and the heat shrinkage rate was calculated using the following formula.

(In the above formula, l ₃ is the transverse or longitudinal length of the porous support specimen before shrinkage, and l ₄ is the transverse or longitudinal length of the porous support specimen after shrinkage.)

-Crosslinking time: 100 mg (W ₀ ) of the support specimen was immersed in 1,2,4-trichlorobenzene and then heat-treated at 130° C. for 2 hours. After separating the specimen and drying it at 50° C. for 24 hours, the weight (W) of the dried specimen was measured and the degree of crosslinking (gel fraction, %) was calculated using the following formula. The time required for the crosslinking degree of each specimen to reach about 60% was measured.

- Meltdown temperature (°C): After applying a force of 0.01N to the porous support specimen and the separator specimen using a thermomechanical analysis, the temperature was raised at a rate of 5°C/min to measure the degree of deformation of the specimen. The temperatures at which the porous support specimen and the separator specimen were broken were set to a meltdown temperature of 1 and a meltdown temperature of 2, respectively.

division Example
One Example
2 Example
3 comparative example
One comparative example
2 comparative example
3 comparative example
4 comparative example
5 Tensile strength (MD) 1,535 1,611 1,692 1,520 1,590 1,626 1,470 1,499 Tensile strength (TD) 1,030 1,081 1,135 1,020 1,090 1,112 1,003 1,023 Tensile Elongation (MD) 67.7 66.3 63.0 67.0 60.0 58.3 75.1 71.7 Tensile Elongation (TD) 52.5 51.5 48.9 52.0 50.0 46.8 62.5 57.9 Thermal Shrinkage (MD) 6.8 6.7 6.5 6.9 5.1 6.3 10.5 10.2 Thermal Shrinkage (TD) 10.9 10.6 9.9 11.0 10.2 9.7 13.4 12.7 Meltdown temperature 1 208 218 224 205 210 216.3 187 194 crosslinking time 50 minutes 30 minutes 20 minutes 72 hours 60 hours 24 hours - - Meltdown temperature 2 233 244 241 230 235 242 209 217

The foregoing description of the present invention is for illustration, and those of ordinary skill in the art to which the present invention pertains can understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present invention. will be. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive. For example, each component described as a single type may be implemented in a distributed manner, and likewise components described as distributed may also be implemented in a combined form.

The scope of the present invention is indicated by the following claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included in the scope of the present invention.

Claims (10)

(a) preparing a porous support by processing a composition comprising a first polyolefin and a second polyolefin modified with a crosslinking compound;
(b) applying steam to the porous support to crosslink the second polyolefin included in the porous support;
(c) preparing a slurry by dissolving the inorganic particles and the binder in a solvent; and
(d) coating the slurry on at least one surface of the porous support and drying to form an inorganic coating layer;
In step (b),
A method of manufacturing a separation membrane wherein the steam is applied in an amount of 1 to 3 kg/m ² for 10 to 30 minutes to adjust the gel fraction of the porous support to 60% or more. According to claim 1,
The first polyolefin has a weight average molecular weight (Mw) of 250,000 to 450,000 g/mol, and a molecular weight distribution (Mw/Mn) of 3 to 7. According to claim 1,
The first and second polyolefins are each selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, ethylene vinyl acetate, ethylene butyl acrylate, ethylene ethyl acrylate, and combinations or copolymers of two or more thereof. A method of manufacturing a separation membrane comprising a. According to claim 1,
The cross-linkable compound is a hydrocarbon-based compound containing at least one alkoxy group and at least one vinyl group, a silane-based compound, or a combination thereof. According to claim 1,
The content of the crosslinkable compound in the second polyolefin is 1 to 50% by weight of the separation membrane manufacturing method. According to claim 1,
The composition further comprises a crosslinking catalyst,
The content of the cross-linking catalyst in the composition is a method for producing a separator of 0.01 to 10% by weight. delete According to claim 1,
In step (b),
Before applying steam to the porous support,
Applying the porous support with a solution containing a crosslinking catalyst,
The content of the crosslinking catalyst in the solution is 0.01 to 10% by weight of the separation membrane manufacturing method. According to claim 1,
In the product of step (b), the first and second polyolefins constitute a continuous phase and a discontinuous phase, respectively,
The content of the second polyolefin in the product of step (b) is 0.1 to 90% by weight of the separation membrane manufacturing method. According to claim 1,
The inorganic particles are SiO ₂ , AlO(OH), Mg(OH) ₂ , Al(OH) ₃ , TiO ₂ , BaTiO ₃ , Li ₂ O, LiF, LiOH, Li ₃ N, BaO, Na ₂ O, Li ₂ CO ₃ , CaCO ₃ , LiAlO ₂ , Al ₂ O ₃ , SiO, SnO, SnO ₂ , PbO ₂ , ZnO, P ₂ O ₅ , CuO, MoO, V ₂ O ₅ , B ₂ O ₃ , Si ₃ N ₄ , CeO ₂ , Mn ₃ O ₄ , Sn ₂ P ₂ O ₇ , Sn ₂ B ₂ O ₅ , Sn ₂ BPO ₆ and a combination of two or more thereof;
The solvent is methanol, ethanol, propanol, butanol, methoxyethanol, ethoxyethanol, lactone, acetonitrile, n-methyl-2-pyrrolidone (NMP), formic acid, nitromethane, acetic acid, dimethyl sulfoxide, distilled water and It is one selected from the group consisting of a combination of two or more of these,
The binder is polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate , Ethylene vinyl acetate, polyimide, polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, hydroxyethyl cellulose , cyanoethyl sucrose, pullulan, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, acrylonitrile-acrylic acid copolymer, ethylene-acrylic acid copolymer, styrene-butadiene copolymer, alkyl acrylate-acrylonitrile copolymer A method for producing a separator selected from the group consisting of coal, polyethylene glycol, acrylic rubber, and a combination of two or more thereof.